The invention is directed to a small commutator motor.
A small commutator motor according to the generic part of claim 1 is known from DE 42 15 504 A1. The small commutator motor described in this reference is used in particular as a fan motor for motor vehicles and has a rotor shaft which is rotatably mounted in a motor housing using rotor bearings; a commutator and an armature winding electrically connected to this commutator are arranged on it so as to be fixed with respect to rotation relative to it. Brushes guided in brush guides are held in sliding contact on the commutator. The rotor bearings are realized as ball bearings and each one is fixed to the rotor shaft by an end shield. These end shields are arranged at the end of the motor housing and mounted on a pole ring. The pole ring serves for the magnetic connection of two permanent magnet poles of a stator surrounding the rotor which are inserted in the pole ring. The pole ring is enclosed by a cylindrical housing body. The brush guides are realized as separate structural component parts and mounted on one of the end shields. For pressing the brushes against the commutator, brush contact pressure springs are provided.
This known small commutator motor has the disadvantage that the end shield next to the brush guides and the brush guides are formed as separate structural component parts, thus increasing the expense for assembly. Another disadvantage consists in the fact that the motor housing is formed by the two end shields, the pole ring connecting the two end shields, and the housing body partially surrounding the pole tube, and thus comprises, in all, four parts. Therefore, the expense for assembling the motor housing is also relatively high.
DE 196 06 487 A1 shows another small commutator motor in a modified construction. The small commutator motor known from this reference has a housing receptacle into which the small commutator motor and a fan wheel driven by the small commutator motor can be inserted. At the same time, the housing receptacle is also used for the air conduction of the intake air flowing towards the fan wheel. In this realization, as well, the housing of the small commutator motor used as the drive motor comprises a pole ring, a housing body surrounding the pole ring, and end shields for fixing the rotor bearings in position, each end shield being connected with the pole ring. The brush guides are also realized as separate structural component parts. The expense for assembly that has already been described is therefore also present in this case.
The small commutator motor according to the invention has the advantage over the prior art that the expenditure on manufacturing and assembly is considerably reduced. Since the end shield situated next to the brush guides is formed as a one-piece structural component part along with the brush guides and is, at the same time, a component part of the motor housing, the result is an extremely compact construction that is easy to assemble. It is no longer necessary to mount the brush guides on the end shield on the one hand and the end shield on the pole ring on the other hand. Rather, the functions of the brush guide, namely, to support of the rotor bearing and housing closure, are integrated in an individual structural component part.
A second end shield provided for a second rotor bearing can advantageously be formed integral with a second motor housing part. In this case, the first motor housing part advantageously closes the second motor housing part like a lid. The two motor housing parts can be produced advantageously as plastic injection molded parts, resulting in low production costs.
The rotor bearings are preferably locked to the associated end shields by ring-shaped holding springs. These holding springs are fixed to the associated motor housing parts, preferably by riveting or by snapping them in position behind projections provided at the respective motor housing part.
It is advantageous for a pole ring connecting at least two poles of permanent magnets with each other to be pressed into the second motor housing part, in which case spacer ribs formed integral with the second motor housing part can be provided between the second motor housing part and the pole ring. Advantageously, these spacer ribs can also be made of an elastomer material; in this case, the second motor housing part can be produced by means of a two-component injection molding process, and the spacer ribs made of an elastomer material can be injection molded onto the second motor housing part. The use of elastomer materials for the spacer ribs results in a particularly low noise emission, since the structure-bome noise emitted by the pole ring is damped extensively.
The axial fixing of the pole ring can be effected either by a stop on the first motor housing part or by special catch hooks forming part of the second motor housing part.
The permanent magnet poles can be fixed advantageously inside the pole ring in that a spring element presses each of the permanent magnet poles against a stop projecting inward at the pole ring. In this manner, possible unavoidable deviations from the correct dimensions resulting from manufacture can be compensated for.
The pole ring is advantageously formed by at least two shells which are separated from one another by gaps running axially relative to the rotor shaft. These shells of the pole ring are substantially more economical and easier to produce than a solid ring. The shells can be made of strip stock using simple tools, for example. The gaps running between the shells have the advantage of suppressing armature cross field.
Advantageously, there can be provided at the second motor housing part an essentially radial flange on which components of control electronics and/or one or more protective resistors can be mounted. In this case, it is particularly advantageous when first metal connections connected to the brushes project radially out of the first motor housing part and second metal connections connected to the components of the control electronics and/or the protective resistors project from the flange of the second motor housing part axially toward the first connections, so that the first and second connections can be connected with one another, for example, by welding, soldering and pressing. The relatively complicated wiring of the control electronics or of the protective resistors to the brushes which has been customary until now is no longer necessary.
If the small commutator motor is driving a fan wheel of a fan, it is advantageous to attach additional blades to the fan wheel in the area of the components of the control electronics or protective resistors for cooling them.
For mounting the fan wheel on the rotor shaft in the motor housing, it is particularly advantageous when the second end shield located opposite to the brush guides has an opening that is closed by a thin membrane or diaphragm. When pressing the fan wheel onto the rotor shaft, the rotor shaft can be supported on the opposite side in that the rotor shaft rests on a suitable counter-piece with the intermediary of the diaphragm. The thin, flexible diaphragm prevents axial forces that occur when the fan wheel is being pressed on from being transferred to the rotor bearing or the motor housing. At the same time, in contrast to an open construction, the flexible diaphragm ensures that the second end shield and the second motor housing part is closed off, so that dirt is prevented from entering the motor housing.